Within the field of watchmaking, a striking mechanism can be combined with a conventional watch movement to act as a minute repeater or to indicate a programmed alarm time. This type of striking mechanism generally includes at least one gong made of sapphire or quartz or metallic material, such as steel, bronze, precious metal or metallic glass. The gong may describe, for example, at least one portion of a circle around the watch movement inside the watch frame. The gong is fixed by at least one end thereof to a gong-carrier, which is in turn secured to a watch plate. A strike-hammer is rotatably mounted on the plate, for example, in proximity to the gong-carrier, so as to strike the gong and cause it to vibrate. The sound produced when the gong is struck by the hammer is within the audible frequency range of 1 kHz to 20 kHz. This indicates to the person wearing the watch a well defined time, a programmed alarm or a minute repeater.
As shown in EP Patent Application No. 1 574 917 A1, the striking mechanism of a watch may include two or more gongs, each fixed via one end thereof to the same gong-carrier, which is in turn secured to a plate. Each gong may be struck by a respective hammer. To achieve this, each hammer is driven by its own drive spring, which must have been pre-wound, so as to drive the hammer against the gong, to indicate a minute repeater or an alarm time. Two damper countersprings are each provided to push back and hold the two hammers away from the gongs in an idle mode. In the strike mode, the damper countersprings act with significant force to slow down the fall of each hammer prior to the strike against the respective gong. After the strike, these countersprings allow each hammer to be pushed back to its idle position. Eccentrics are also provided for adjusting the operation of the countersprings essentially to prevent each hammer from rebounding against the respective gong.
One drawback of this type of striking mechanism structure with countersprings is that there is a significant loss of kinetic energy when the hammer strikes the respective gong, which reduces the acoustic level of the striking work. This energy loss is largely due to the slowing down imposed by each counterspring on the path of the hammer when it strikes the gong. Moreover, even if the pre-winding of the drive springs is increased, this involves adapting the countersprings via their eccentric, also to prevent any rebound, which is another drawback of this type of striking mechanism.
EP Patent Application No. 1 394 637 A1 also discloses a striking mechanism fitted with at least one gong and a hammer capable of striking the gong at determined times. This striking mechanism further includes a control device which, on the one hand, provides a visual indication of the active or inactive state of the mechanism, and, on the other hand, can lock or unlock the hammer via a push-button. When the hammer is in an unlocked state in the strike mode, there is nothing to prevent the hammer rebounding against the gong following the first strike of the hammer against the gong, which is a drawback.